The Sahara, the largest hot desert in the world, is still getting bigger. In fact, it’s currently about 10 percent larger than it was almost a century ago, and scientists suggest climate change is partly to blame.

In a new study, researchers looked at rainfall data collected across Africa, looking at records dating back to 1920 and noting how changing conditions were affecting regions around the edges of the great desert.

They found that while certain natural climate cycles could partly explain the reduction in precipitation and the desert expansion southward, human-induced climate change also plays a role. And if climate change continues unchecked, the Sahara’s slow growth is likely to continue, the study’s authors reported. [The Sahara: Facts, Climate and Animals of the Desert]

Previously, scientists had explored the expansion of the Sahara by examining satellite data dating back to the 1980s. This study, which was supported by the National Science Foundation in the United States, is the first to analyze long-term trends in precipitation. and surface air temperature over a time scale of nearly a century, said lead author of the study, Natalie Thomas, a doctoral student in ocean science at the University of Maryland, said declared Live Science.

Deserts are defined as places on Earth that receive less than 10 inches of precipitation per year, according to the US Geological Survey (USGS). With an area of ​​approximately 3.6 million square miles (9.4 million square kilometers), the Sahara is the third largest desert in the world. Only cold deserts are bigger: the frozen desert of Antarctica covers about 5.5 million square miles (14.2 million square kilometers) and the arctic desert covers about 5.4 million square miles ( 13.98 million square kilometers), the USGS reported.

“A strong expansion”

The study’s authors had initially set out to examine seasonal cycles of temperature and precipitation across Africa, looking at data from 1920 to 2013. But their attention was quickly drawn to declining trends in rainfall. rainfall in the Sahel, a semi-arid region connecting the Sahara to the savannas of Sudan. . Upon closer inspection, they hoped to find out how rainfall trends might be related to the growth of the Sahara over time, according to Thomas.

To some extent, the boundaries of many deserts expand and contract seasonally, with conditions fluctuating between wetter and drier. But researchers have found that there has been “a strong expansion” of the Sahara during the 20th century, Thomas said.

Depending on the season, the Sahara has grown by at least 11 percent, and it has increased by up to 18 percent during the driest summer months, according to data collected over about 100 years. Over the course of a century, it gradually expanded to become about 10 percent larger than it was in 1920, the study’s authors reported.

Much of the increase in the overall size of the Sahara can be explained by climate cycles driven by anomalies in sea surface temperatures. These cyclical changes in turn affect surface temperatures and precipitation on land, and their impact can last for decades, according to the study.

Decades of drought

One of these cycles, the Atlantic Multidecadal Oscillation (AMO), entered what is called a “negative phase” – with colder than average sea surface temperatures – in the 1950s. , bringing heat and dry conditions to the Sahel region and fueling a drought that lasted until the 1980s, Thomas said.

Using statistical methods, the scientists compensated for the effects of AMO on average precipitation and thus calculated to what extent the growth of the Sahara could be explained by the drought produced by the negative phase of the cycle. They estimated that AMO accounted for about two-thirds of the expansion of the desert, but one-third of the remaining growth in the Sahara was likely the result of climate change.

The researchers’ findings indicate changes that occur over decades rather than a single year, making it difficult to predict exactly how the Sahara’s continued growth might affect wildlife and people near its shifting borders. But as the places where humans grow food become drier and drier, some areas could become more vulnerable to drought, which would increase the risk of starvation for the people who live there, Thomas said.

The results were published online today (March 29) in the Journal of Climate.

Original article on Live Science.